CMOS-based information processing methods are expected to be limited for the following reasons. Firstly, the thickness of a gate oxide layer should be gradually decreased as an integration degree is improved. However, when the thickness of the gate oxide layer is about 0.7 nm, electrons transmit the gate oxide layer and the gate oxide layer does not serve as an insulating layer any more. Secondly, when the widths of conducting wires are reduced for improvements in the integration degree, a short of the conducting wires occurs due to an increase of current density.
In order to replace CMOS-based information processing methods, a study for information processing methods using spins which are quantum characteristics of electrons, has been made breaking from information processing methods by electrons, that is, the movement of charges. For example, a study for a magnetic quantum cell automatic device using soliton in nano magnetic materials and a study for spin waves generated in magnetic materials to transmission and processing of information have been made.
Spin waves mean that spins make collective movements in the shape of waves. When an energy is applied to magnetic materials such as ferromagnetic materials, antiferromagnetic materials or ferrimagnetic materials, spins inside the magnetic materials make a precessional motion, and precessional motions of respective spins are wave-shaped by a magnetic interaction between the spins, such as dipole-dipole interaction or exchange interaction. The waves are spin waves.
Spin waves are classified into several types of waves according to dominant interactions: a first type is a magnetostatic wave in which a dipole-dipole interaction acts dominantly and which has a wavelength of several μm to several cm; a second type is an exchange spin wave in which an exchange interaction acts dominantly and which has a wavelength of less than several nm; and a third type is a dipole-exchange spin wave in which two interactions act competitively and which has a wavelength of several nm to several μm. The magnetostatic wave has been currently studied for applicable aspects and has been used for a device for high-frequency signal processing.
A method of generating spin waves used in an existing magnetostatic wave device is as follows (for example, U.S. Pat. Nos. 4,208,639, 4,316,162 and 5,601,935). When an electromagnetic wave is generated by flowing a high-frequency alternating current (AC) through a conducting wire formed on a thin film surface of ferrimagnetic materials such as YIG, a high-frequency magnetostatic wave is generated due to strong coupling of the generated electromagnetic wave and a magnetostatic wave of ferrimagnetic materials and travels toward an inside of the magnetic material. The wavelength of the magnetostatic wave generated in this way usually has the size of 10 μm to 1 mm. The core of this method is to apply a magnetic field to a local area of the magnetic material through a conducting wire and to generate and to propagate spin waves.
The wavelengths of spin waves should be several nm and the frequencies of the spin waves should be equal to or greater than GHz so that an information processing device using spin waves becomes a new-concept ultra-high speed information processing device for replacing an existing CMOS-based information processing method, and the generation of spin waves locally should be possible in a several nm to several hundreds of nm-size area of a device. However, since an induction field due to a current flowing through the conducting wire is formed to a size that is in inverse proportion to a distance even in a distant area from the conducting wire, in a device using an existing magnetostatic wave, all areas of the device are included in the effect of a magnetic field and spin waves cannot be generated in a local area.
Thus, a method of generating dipole-exchange spin waves is firstly needed for an information processing device using spin waves. However, a study for using exchange spin waves and dipole-exchange spin waves in a device has proceeded hardly. Japanese Patent Laid-open Publication No. Hei 6-097562 discloses a conceptual method of generating spin waves by causing a change of a magnetic interaction inside a magnetic material by applying an energy to the magnetic material, and an example thereof is a method of making spin waves in a bottom state into an excitation state by radiating Cu—K X-rays to the magnetic material. However, a method of generating spin waves by the supply of the energy presented here is just a general method of generating spin waves in a magnetic material, and a method of generating strong spin waves in a local area for the use in an information processing device for spin waves has not been presented.